1. Field of the Invention
The present invention relates to an image forming apparatus and an image forming method.
2. Description of the Related Art
In an image forming apparatus, a quantity of light on an exposed surface is affected by characteristics of a deflecting element, which deflects light beam, and a lens, so even when a light source emits light beam at a constant light quantity, the light beam onto the exposed surface is not constant in light quantity. Consequently, there is a variation in an electrostatic latent image on a recording medium, and a developed image is lacking in uniformity, which shows up as perceived banding on a finally-formed image, whereby an image quality is affected.
In a conventional image forming apparatus, an image quality is improved with use of an optical element, for example, by using a lens having a characteristic capable of preventing a light quantity on the exposed surface from varying or by placing a filter on an optical path. In addition, a shading correction is performed by performing pulse-width modulation or phase modulation of a drive voltage of a light-source drive element (for example, see Japanese Patent Application Laid-open No. 2002-172817).
However, in a method for improving an image quality with use of an optical element, it is hard to adapt a temporal change due to degradation of the optical element and the like.
Furthermore, in a case of a shading correction, correction characteristics represents a continuous correction curve in accordance with optical characteristics of a lens and the like as shown in FIG. 11, so if the shading correction is performed by the pulse-width modulation of a drive voltage of a light-source drive element, the number of gradations has to be increased, and in a configuration of an apparatus, for example, it brings an excessive increase in Look Up Table (LUT) or an excessive increase in circuit size for high-speed processing and the like.
Moreover, if the number of gradations is small, the correction curve is not smooth and has steps as shown in FIG. 12, which contributes to an uneven image around the steps, and furthermore, it is necessary to provide a filter element on the outside, and the apparatus configuration increases excessively.
Furthermore, when the shading correction is performed by the phase modulation, in the same manner as the pulse-width modulation, if the number of gradations increases, there is a problem of an excessive increase in circuit size.